Recently a new type of fluid compressor, i.e., an axial flow fluid compressor, has been developed to seek for ease of fabrication and assembling, as well as to seek for a simple construction, a good sealing of refrigerant gas and a high efficiency of compressing. Of such axial flow fluid compressors one having two blades on a rotary member, as shown in FIG. 1, has been developed. The axial flow fluid compressor of FIG. 1, which has been developed by the same inventor of this application, is disclosed in the Japanese Patent Disclosure P02-19684 opened to public on Jan. 23, 1990.
In FIG. 1, the axial flow fluid compressor 1 includes a harmetically sealed casing 2, an electrical driving element, e.g. a motor 3 and a compressing element 4.
The casing 2 comprises a sleeve 2a having a base 2b unitarily closing one end of the sleeve 2a. The sleeve 2a securely fits therein a stator 3a of the motor 3, while the base 2b of the casing 2 secures a main bearing 7 thereto for rotatably supporting rotating members of the motor 3 and the compressing element 4. This results to make a prescribed compressing space in the cylinder 5.
The compressing element 4 comprises a cylinder 5 and a rotary member 11 with a columnar shape. The cylinder 5 is coaxially secured to the inner peripheral surface of the rotor 6 of the motor 3 so as to rotate together with the rotor 6. One end of the cylinder 5 is rotatably fitted on an outer peripheral surface of the main bearing 7 at a sufficiently sealed condition. Another end of the cylinder 5 is also rotatably fitted on an outer peripheral surface of a sub bearing 9 at a sufficiently sealed condition, the sub bearing 9 being suspended on a supporting plate 8. The supporting plate 8 is fitted on the open end of the sleeve 2a. Thus the cylinder 5 is rotatably supported its both ends by the main bearing 7 and sub bearing 9. The sub bearing 9 is fastened to the supporting plate 8 with screws 10 to avoid the sub bearing 9 being loosed from the supporting plate 8 during an assembling operation of the axial flow fluid compressor 1.
The cylinder 5 contains therein a rotary member 11 with a columner shape. The rotary member 11 is rotatably suspended at its two shaft ends 11a, 11b by the main bearing 7 and the sub bearing 9, respectively. That is, the shaft end 11a is rotatably fitted into a bearing hole 7a of the main bearing 7, while the other shaft end 11b is rotatably fitted into a bearing hole 9a of the sub bearing 9. The bearing hole 7a and the bearing hole 9a are eccentric from the axis of the cylinder 5 by a prescribed distance e. So that, the outer peripheral surface of the rotary member 11 partially contacts with the inner peripheral surface of the cylinder 5 along a line longitudinal to the axes of the rotary member 11 and the cylinder 5.
A power transmission mechanism 12 is coupled between the cylinder 5 and the rotary member 11 at the position near the sub bearing 9. The power transmission mechanism 12 drives the rotary member 11 when the cylinder 5 is driven by the motor 3, so that the rotary member 11 is caused a relative rotation in regard to the cylinder 5.
The outer peripheral surface of the rotary member 11 is defined a pair of spiral grooves G, G with a prescribed sectional shape, thus resulting the compressing element 4 to be functionally divided into two symmetrical compressing sections. Thus the compressing space in the cylinder 5 is also divided in two compressing sub-spaces The spiral grooves G, G turn in the opposite directions with each other, and their spiral pitches gradually narrow from the intermediate portion of the rotary member 11 along its axis toward its respective end portions. The spiral grooves G, G are provided therein with a pair of spiral blades B, B. The spiral blades B, B have sectional shapes and spiral pitches corresponding to those of the spiral grooves G, G. The spiral blades B, B are not only movable in the spiral grooves G, G in the radial direction of the rotary member 11, but also intimately contacts with the inner peripheral surface of the cylinder 5.
According to the arrangement of the compressing element 4, in each of the two symmetrical compressing sections the compressing sub-space in the cylinder 5 is further partitioned to a plurality of working chambers C by the cooporation of the spiral blade B and the longitudinal contact between the cylinder 5 and the rotary member 11. The volumes of the working chambers C decrease from the intermediate portion to the end portions of the rotary member 11, in proportion to the spiral pitch of the spiral groove G and the spiral blade B.
The bearing hole 7a of the main bearing 7 opens to an inlet tube 13 which is coupled to a refrigeration cycle (not shown), while the rotary member 11 is provided with an inlet opening 14 which elongates from the end of the shaft end 11a facing the inlet tube 13 to the outer peripheral surface of the rotary member 11 at the intermediate portion of the rotary member 11. Thus a refrigerant gas is introduced into the compressing space between the cylinder 5 and the rotary member 11 from the inlet tube 13 through the inlet opening 14. The refrigerant gas then separately propagates to the working chambers C of the two symmetrical compressing sections. The compressing element 4 is also provided with a pair of outlet openings 15, 15 on the respective ends of the cylinder 5. The outlet openings 15, 15 couple the outermost working chambers C to a buffer space defined between the compressing element 4 and the casing 2. Thus the refrigerant gas compressed by the compressing element 4 is discharged into the buffer space in the axial flow fluid compressor 1. The refrigerant gas is then discharged from the axial flow fluid compressor 1 to the refrigeration cycle through a discharge tube (not shown).
Now the operation of the axial flow fluid compressor 1 will be described. The motor 3 drives the cylinder 5 to rotate. The rotation of the cylinder 5 is transmitted to the rotary member 11 through the power transmission mechanism 12. When the rotary member 11 rotates in relative to the cylinder 5, each of the spiral blades B, B also rotates together with the rotary member 11. Since the outer surface of the spiral blade B intimately contacts with the inner peripheral surface of the cylinder 5, when a portion of the outer peripheral surface of the rotary member 11 is getting closer to the inner peripheral surface of the cylinder 5, a corresponding portion of the spiral blade B is depressed into the spiral groove G. On the other hand, when the portion of the outer peripheral surface of the rotary member 11 is getting far from the inner peripheral surface of the cylinder 5, the corresponding portion of the spiral blade B rises up in the spiral groove G.
On the other hand, a refrigerant gas is sucked into the axial flow fluid compressor 1 through the inlet tube 13. The refrigerant gas is then introduced to the intermediate portion of the compression space in the compressing element 4 through the inlet opening 14, so that in each of the two symmetrical compressing sections some amount of the refrigerant gas is locked in the working chamber C close to the intermediate portion. The working chamber C moves toward the end portion of the rotary member 11 along with the rotation of the rotary member 11, while the volume of the working chamber C decreases along with the movement of the working chamber C. As a result, the refrigerant gas in the working chamber C is compressed up to a prescribed pressure when the working chamber C reaches the position facing the outlet opening 15. the compressed refrigerant gas then discharged into the buffer space in the casing 2 through the outlet opening 15 of the cylinder 5.
The prior art axial flow fluid compressor described above, however has a problem of a pressure unbalance as follows. That is, the shaft end 11a facing the inlet tube 13 is subjected to the suction pressure of the refrigerant gas. While the other shaft end 11b facing the sub bearing 9 is subjected to the discharge pressure in the discharge space. The pressure difference between the suction pressure and the discharge pressure causes a thrust force against the rotary piston 11 in the direction from the sub bearing 9 to the main bearing 7. According to this thrust force, the shaft end 11a of the rotary member 11 presses against the main bearing 7. This causes a serious problem of poor lubrication in the bearing systems of the compressing element 4, especially in the main bearing 7. Furthermore, the axial flow fluid compressor 1 is reduced its compressing efficiency due to the thrust force.
Furthermore the prior art axial flow fluid compressor has a problem of that in the assembling process of the compressor the positioning of the compressing element in the casing is very difficult.